1. Field of the Invention
The present invention relates to a burner having a swirl generator.
2. Discussion of Background
A problem exists in the case of swirl-stabilized burners, as disclosed, for example, from U.S. Pat. No. 4,932,861 to Keller et al. as a premixing burner, if a liquid fuel is injected along the burner axis. The liquid column forming downstream of the fuel nozzle acts, particularly in the initial region downstream of the injection, in the same way as a solid body for the combustion air stream flowing tangentially into the interior of the premixing burner. In comparison with the flow without the injection of liquid fuel, the inflow of combustion air in the burner head is impeded, with the result that the tangential component of the swirl flow increases. This leads to a change in the flame position, which travels further upstream. If a further injection of a fuel is carried out along the tangential air inlet slits, then such fuel injection becomes extremely hazardous to operate, because a flame front acting in this region leads unavoidably to a flashback into the system. Furthermore, there is an enrichment of the flame center, which impairs the operation of such a premixing burner in many ways. In such operation, various disadvantages may arise, and these can be listed below, albeit not conclusively:
a) There is an increase, which cannot be underestimated, in the risk of a flashback, and this may easily lead to a burnup of parts of the premixing burner. If this occurs, there is a potential risk, inasmuch as parts which crumble away may cause serious damage to the machine;
b) Operation in an optimum flame position with a liquid fuel should not be designed to be over a wide range for safety reasons, and therefore the premixing burner has a small operating range;
c) The absence of integral intermixing from the outset between the spray cone and the combustion air stream leads unavoidably to an increase in the NOx emissions for the reasons mentioned above;
d) Furthermore, the inhomogeneous mixture distribution leads to further disadvantages which cause increased pollutant emissions and the generation of pulsations;
e) There are pronounced deviations from the optimum flow conditions for reliable and efficient combustion.